1. Field of the Invention
The present invention relates to a tire building drum for building a green tire from a green case or a carcass band composed of members including a carcass member of a tire.
2. Description of the Related Art
In a green tire building process, a cylindrical carcass band or green case is generally built on a first building drum, a cylindrical belt tread band is built on a second building drum by bonding a belt member with a tread rubber, and then the cylindrical carcass and the cylindrical belt tread band are respectively transferred onto a green tire building drum. Subsequently, while holding both bead cores of the carcass band or the green case in place, the main body of the carcass member extending between the bead cores is swelled radially outwards to contact a cylindrical inner side of the belt tread band placed outside thereof, so that the main body and the belt tread band are tightly attached to each other by pressure.
A green tire building apparatus for use in such a process has a pair of bead lock sections for holding both bead cores, and a center bladder for sealing spaces defined between the bead lock sections, wherein the center bladder is entirely made of rubber. The main body of the carcass member can be toroidally swelled radially outwards by pressurizing the center bladder and thereby applying inner pressure to the space.
In this building process, the rubber bladder is assigned primarily with a sealing function, so that the main body of the carcass member itself is designed to support the inner pressure and determine the shape of the swelled main body of the carcass member. While this process is widely used due to its advantage in terms of cost, which results from use of the rubber bladder, there is a potential problem that the uniformity of the product tire tends to deteriorate if any portion with uneven strength is present in the main body of the carcass member such that the main body of the carcass member assumes uneven shape when it is swelled.
For improving the uniformity of the product tire, it is important to ensure that the main body of the carcass member has a swelled shape that is as close to the shape of the product tire as possible, already at the green tire building stage so as to minimize deformation of the green tire during vulcanization. However, this is practically difficult to realize by the above-mentioned prior art process, since the swelled shape is uniquely determined by the strength distribution in the main body of the carcass member.
In order to address such a problem, JP-A-8-011239 proposes a method wherein the building drum has a center bladder embedded with cords, so as to determine the swelled shape of the main body of the carcass member by applying tension to the cords. An additional or alternative measure is proposed in EP-A-0661151 or U.S. Pat. No. 5,164,035, for example, wherein a building drum is provided, instead of, or in addition to the center bladder, with a plurality of rigid bodies in the form of metal segments abutting on each other in the circumferential direction and made radially expandable/contractible so as to determine the swelled shape of the carcass member when expanded.
These known tire building drums can accurately realize a desired swelled shape of the main body of the carcass member, which is nearly the same as the product tire so as to advantageously improve the uniformity of the latter. From practical viewpoint, however, there is a problem that the prior art processes as mentioned above are not very suitable for continuously building tires in various dimensions with a single tire building drum. That is, for a production of tires having various dimensions with known tire building drums, it is necessary to frequently replace the building drum or the segment of the drum. Since these replacements are time-consuming, the known tire building drums are practically applicable only to a batch production in a large lot, which requires few dimensional changes. As a result, a large amount of intermediate stock have to be carried and stored, which result in disadvantages in both space and cost. Therefore, in order to overcome these problems, it would be desirable to provide a tire building drum capable of various dimensions, namely, a tire building drum which can continuously produce tires in various dimensions with a desired sequence, without replacing its parts.